Knee joint for prostheses



Oct. 26, 1948. o. l. FAHLSTRC5M KNEE JOINT FOR PROSTHESES 2 Sheets-Sheet 1 Filed April 28, 1944 Oct. 26, 1948- o. 1. FAHLSTRbM KNEE JOINT- FOR PROSTHESES Filed April 28, 1944 2 Sheets-Sheet 2 Patented Oct. 26, 1948 OFFICE KNEE JOINT FOR PROSTHESES Otto Ivan Fahlstriim, Stockholm, Sweden Application April 28, 1944, Serial No. 533,142 In Sweden January 10, 1942 7 Claims.

Prostheses are, particularly nowadays, used to a very great extent. It is evidently of great importance that the prostheses are constructed in such a way that they operate as perfectly as possible, and it is of particular importance that the mutual movements of the prosthesis members at changes of position when walking and so on are as equal as possible to the movements of the cor responding natural limbs and as little as possible are subjected to irregularities in the function.

The present invention relates to a knee joint for a prosthesis and is illustrated on the accompanying drawing, in which Fig. 1 shows the shin member and the thigh casing when the leg is straight.

Fig. 2 shows the position when beginning to walk.

Fig. 3 shows the position of the joint when sitting.

Fig. 4 is a view of the leg at right angles to the other figures.

In all of the four figures the shin member is shown in section.

The hollow shin member 2 is fixed to the thigh casing I, which is formed in the manner described below, by means of the knee joint according to the present invention. The back of this casin is formed as a nose 3 at its lower end when the leg is straight, this nose engages a concave member If) on the mounting frame 4 fixed to the inside of the shin member 2 by means of screws 6. The thigh casing l and the shin member 2 are movably connected by means of a substantially U- shaped yoke, the legs I of which form two links connected at their upper ends with the thigh casing l by means of ball-bearings 8 and intermediate their ends with the side walls of the mounting frame 4 by means Of ball-bearings 8. The yoke legs extend some distance downwardly into the mounting frame, and are connected at their lower ends by the transverse portion 7' of the yoke. This transverse yoke portion 1 moves according to the difierent positions of the thigh and the shin member, between stops 9 and 9, as will be described more particularly below. As shown in the drawing, two stops 9 and two stops 9 are located adjacent the side walls of the frame 4 (see Fig. 4) to cooperate with the corner portions of the transverse yoke member I.

In continuation of the inner stopping surface of the abovementioned concave member Hi there is provided on the mounting frame 4 a guide surface 5 along which the nose 3 of the thigh casing is adapted to glide when, under the influence of 2 the thigh member l2 (see Fig. 4) and the thigh casing I, the nose leaves the concave member I0, see Fig. 2. i

The joint is constructed in such a way that the transverse portion 1' of the yoke member is under the influence Of a force, such as a spring, which tends to move the lower portion of the yoke to the left, i. e, to swing the same clockwise in the ball bearing 8, see Fig. 1. For this purpose a tension spring ll pulling to the left has been shown on the drawing.

Standing with a straight leg, the yoke leans backwards, Fig. 1, and due to the stops 9 and 9 the leg does not bend when subjected to load. But when one is beginning to walk and the leg has assumed the position according to Fig. 2 with the shin member leaning forwards the upper leg presses upon the yoke 'l in such a, way that the yoke is swung counter-clockwise against the influence of the spring I I so that the transverse part I of the yoke strikes against the stops 9. The nose 3 of the thigh casing slips then out from its position in the concave member [0 and the leg can be bent for walking or sitting. It is evident that, when walking for example, the movements of the foot must be suited to those of the leg. The position of the knee-joint when sitting is shown in Fig. 3 where, after the nose 3 has left the guide surface 5, the transverse portion of the yoke member I has reassumed its normal position resting against the stop 9'. and the upper portion of the thigh casing can rest against the outer surface of the concave member ID.

The details of the device described above and illustrated on the drawing may, of course, be varied in some way or other with regard to the number, the material and the construction without going beyond the scope of the invention. The device may preferably be made of light metal, but any other material may be used.

Havin now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A knee joint for prostheses comprising a link swingably connected intermediate its ends with the shin member at each side of the joint, the upper ends of the said link being jointed to the thigh casing of the prosthesis, and resilient means urging the lower ends of said links towards the front of the shin member.

2. A device as claimed in claim 1, including ball bearings] connecting the upper ends of the links with the thigh casing.

3. A device as claimed in claim 1, including ball bearings connecting said two armed levers intermediate their ends with the shin member,

4. A device as claimed in claim 1, including a nose formed at the back of the thigh casing, a mounting frame fixed to the inside of the shin member, and a concave member on said mounting frame to be engaged by said nose at the back of the thigh casing when the leg is straight.

5. A device :as claimed in claim 1, including a mounting frame "fixed; to the'insideof the shin member, the said mounting frame having stop means against which the lower portions of said links are urged by said resilient means and other stop means adapted to limit the swinging movement of the links in the direction away from said first-mentioned stop means upon bending of the leg.

6. A device as claimed in claim 1, including a nose formed at the back of the thigh casing, a mounting frame fixed to the inside of the shin member, the said mounting frame havin on top of its rear walla concave member to be engaged by said nose at the back of the thigh casing 4 when the leg is straight and below said concave member a curved guide surface along which said nose glides upon transition from straight to bent leg, the back of the thigh casing and the concave member being located in such a way relatively to one another that when sitting the thigh casing rests on the outer surface of said concave member.

'7. A device as claimed in claim 1, including a transverse member connecting said links at their lower ends and forming with said links a substantially U-shaped yoke, said resilient means being a spring acting upon said transverse member.

OTTO IVAN FAHLSTROM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,365,205 Stinehart Jan. 11, 1921 1,447,230 Winn Mar. 6, 1923 

